The invention relates to a magnetic resonance (MR) method for forming an image of an object from a plurality of signals sampled in a restricted homogeneity region of a main magnet field of the magnetic resonance imaging apparatus, whereas a patient disposed on a table is moved continuously through the bore of the main magnet, such that an image is formed over a region exceeding largely the restricted region of a main magnet field of the magnetic resonance imaging apparatus.
The invention also relates to an MR apparatus and a computer program product for carrying out such a method.
Since it is quite uncomfortable for a patient being disposed in a large bore of the main superconductive magnet of an MR imaging apparatus, there is a trend to use shorter magnets while moving the patient table or couch through the bore of the magnet. Such an apparatus is described e. g. in U.S. Pat. No. 6,385,478. In an MR imaging apparatus excitation pulses are applied to a restricted region of the magnet bore, in which the field is uniform. The data samples collected are Fourier transformed to form a volumetric image of the restricted region. A motor continuously moves a patient couch so that a region of interest passes through the region of good field. The collected data samples are corrected to compensate for the motion so that a volumetric image is formed of greater length than that of the restricted region.
The MR imaging as mentioned above takes quite a long time since it is performed with conventional imaging sequences and even an overlap between successively imaged volumes is preferred in order to discard artefacts produced by errors in the central region. Obviously, the r.f. transmit coil and the r.f. receive coil are disposed in the reference frame of the main magnet, i.e. in its direct vicinity. However, imaging by body coils disposed on different places of a patient was not an issue in this reference. Anyway, it is known that using body coils may cause additional artefacts which cannot be suppressed in an easy manner.